1. Field of the Invention
This invention relates to photographic cameras, and more particularly to focal plane shutters of the two-curtain type. Still more particularly, it relates to improvements in accuracy and reliability of electromagnetic shutter release actuation control.
2. Description of the Prior Art
The conventional focal plane shutters of the two-curtain type are generally provided with separate latches of which, though one for the opening or front curtain is rendered effective to hold that curtain in cocked position after one cycle of film winding operation is terminated, the other latch for the closing or rear curtain is used to become effective soon after the start of movement of the front curtain, as the rear curtain has so far been retained by a reset bar. During the winding process, this reset bar serves to transmit driving torque from the front curtain wind-up drum to the rear curtain wind-up drum, regardless of whether these drums are mounted in coaxial relation as, for example, disclosed in U.S. Pat. No. 3,633,480, or in off set relation but with their drive gears being coaxial to each other, as, for example, disclosed in U.S. Pat. No. 2,961,934. In any case, this reset bar takes the form of a pin extending from the front curtain cocking drive gear into the path of movement of a projection on the rear curtain cocking drive gear.
Such a reset mechanism for the shutter, though having several advantages such as simple structure and easy operation of "B" exposure, gives rise to a problem of diminishing the accuracy and reliability of high speed exposure control when an operating member for the rear curtain is constructed in the form of an electromagnet. As the attractive force established between the core of the electromagnet and the armature on the rear curtain latch is adjusted to slightly exceed the separating force exerted on the latch by the biasing action of spring means, when the reset bar is moved away from the rear curtain wind-up drum to permit shocking abutment of the latter against the latch therefor, the accuracy and reliability of actuation control of the rear curtain tend to be diminished to a large extent particularly in taking an exposure with as a high shutter speed as 1/2000 sec.